1. Field of the Invention
This invention relates to a water pump apparatus, and more particularly to a water pump apparatus which is used in an internal combustion engine of a water cooled type and includes lubrication of a sliding bearing surfaces for the pump rotational shaft.
2. Description of the Related Art
A conventional apparatus of this type is, for example, disclosed in Japanese Utility Model Laid Open No. 61-10997.
As shown in FIGS. 5 and 6, in which the conventional water pump apparatus is described, an impeller 4 is fixedly connected to one end of a drive shaft 35 supported on a body member 31 and the drive shaft 35 is rotated by an external power means via a gear 34. The drive shaft 35 is directly supported in an inner hole 32 provided in the body member 31. In order to lubricate the sliding surface between drive shaft 35 and the inner hole 32, concave portions 33, 33 are provided at upper and lower portions of the body member 31 to retain lubricating oil, and oil seals 36, 36 are positioned at the ends of the concave portions 33, 33 in order to seal the oil in the concave portions. These concave portions 33, 33 communicate with each other via a sliding surface between the inner hole 32 and the drive shaft 35, and another communicating passage is not positively provided.
The oil sealed in the concave portions 33 is thus circulated only via the sliding bearing surfaces between the inner hole 32 and the drive shaft 35, so that the circulation of the oil is not smoothly performed. As a result, the surface of the drive shaft is subjected to oxidative deterioration and the drive shaft 35 is sometimes seized Further, the oil sealed in the concave portion 33 is not perfectly sealed by oil seals 36, 36, so that oil leakage past the oil seals 36, 36 may occur due to the pressure increase generated by thermal expansion during rotation of the drive shaft 35.
The thrust force created by the rotation of the impeller 4 is supported only by the gear 34, so that the water pump apparatus is restricted only to such gear drive, unless a mechanism for maintaining the thrust force is provided at an outer portion of the water pump. As a result, the applicable field of this type of water pump apparatus is restricted.